There are many people who get killed in traffic accidents. Theft and burglary using cars/motorcycles have been repeatedly reported. These may be attributed to poor image identification of license plates because of poor monitoring systems. Such monitoring systems are mostly problematic because of poor resolution (320×240 Pixels) and slant angles of the image acquiring units to cause blur or incomplete images that cannot be recognized so that the criminals can be at large.
Conventionally, in Taiwan Patent No. 197752, a CCD camera and an image acquiring unit are used to acquire a car image in the car lane and the car image is then read by an image reading unit. Then, a logarithmic greyscale operation unit is used to calculate the logarithmic greyscale of each pixel in the car image. The image corresponding to the logarithmic greyscales is decomposed by a wavelet decomposition unit into rough images, horizontally differentiated images, vertically differentiated images and diagonally differentiated images. An image binarization unit converts the logarithmic greyscale of each pixel in the horizontally differentiated images from real numbers into binary digits 0 and 1. A rough image dividing unit determines a region with the highest sum of binary digits within the whole car image according a pre-set license plate size and thus the region is initially referred to as a license plate region. Then, a license plate slantness correction unit corrects the slantness of the image corresponding to the license plate region. Finally, a fine image dividing unit removes the part that does not correspond to the license plate from the rough license plate region.
Moreover, in Taiwan Patent Pub. No. 1286027, an integrated plurality of lane free flow vehicle enforcement system is disclosed, wherein a portal framed equipment is established at the image enforcement point. The car lane is physically divided so that image enforcement can be realized with respect to various cars even though the system slows the cars to pass by the image enforcement point at a normal speed and to change lanes freely.
Moreover, in Taiwan Patent Appl. No. 200802137, a serial license plate identification system is disclosed, using a license plate character region detection module to receive an image and determine each approximate license plate range in the image. Sequences of serial identical pixels in each approximate license plate range are obtained. The sequences of serial identical pixels are erased, filtered, and connected to blocks so as to obtain the image with respect to the license plate character region in each approximate license plate range and output verified image with respect to the license plate character region after verification. Then, the verified image with respect to the license plate character region is transmitted to the a license plate character dividing and identification module to acquire all the independent character images and thus all the license plate character information after the independent character images are identified.
Moreover, Taiwan Patent No. 221193 discloses a license plate identification and monitoring apparatus used in a parking area. When a car passes by a pre-determined image acquiring spot, the host is informed to enable the duplex image acquiring device to control the camera device to acquire the car license plate image, which is then processed by the an identification process to identify the characters on the license plate for car management, stolen car seeking and prevention in the parking area.
Taiwan Patent No. 226454 discloses a license plate identification method, wherein the logic relation and character strokes are used to determine the correct license plate location in the digital image. Then, ternarized difference and fuzzy inference are used to acquire the outlines of the characters on the license plate. Adaptive binarization method is used to divide the boundaries of each character. Finally, the identification result can be obtained by a feature fused median calculation using a neural network.
Moreover, Taiwan Patent No. 191905 discloses a automatic mobile license plate identification system, which comprises an image acquiring device and an image processing device that can be installed in a car to perform automatic identification on a static or moving car being monitored. The image acquiring device is capable of acquiring the image of the license plate and transmitting the image into the image processing device. The image processing device performs a precise acquiring process on the license plate characters based on fuzzy inference and performs a character identification process on the characters using character structure analysis. Therefore, identification errors due to license plate contamination, bending, character contamination or deflexion can be prevented.
Taiwan Patent No. 123259 discloses a license plate number identification apparatus installed at a spot where cars pass by so as to automatically identify the license plate number of a car. The license plate number identification apparatus uses an image acquiring device capable of acquiring an image containing the license plate and an image processing unit capable of checking the digital image according to features of the license plate number to find the license plate location, specify the range of characters, divide the characters to achieve feature identification of each characters.
Moreover, U.S. Pat. No. 4,817,166 discloses a method for reading a license plate by acquiring the boundary features such as length, height, and width of the characters on the license plate. With such information regarding the character features, geometric features of the characters such as the locations and shapes of convex hulls, turns and holes are analyzed. Finally, the structure of each character on the license plate is analyzed according to the results of the aforegoing analysis.
Moreover, U.S. Pat. No. 6,553,131 discloses an identification technology using a smart image acquiring device to perform license plate identification. A processor is installed inside the image acquiring device to perform license plate information identification. In this technology, image identification is implemented by determining a base line according to the brightness and location of the license plate image and a blur region. The image having a base line is then processed by projection to obtain the location of each character on the license plate. A statistic-based method is used so that each character is provided with a confidence index. Finally, character information on the license plate is determined according to the confidence index.
Moreover, U.S. Pat. No. 5,425,108 discloses a license plate image identification technology, wherein the acquired license plate image is processed by fuzzy interfere and the features of the license plate image is identified by structure analysis using a neural network features.
Moreover, U.S. Pat. No. 6,473,517 discloses a license plate identification technology, wherein the license plate image is identified by character segmentation. In this technology, the license plate image is divided into a plurality of regions to be converted into possible character regions (or suspected character regions). Then, the possible character regions are identified to obtain a confidence index for image identification based thereon.
U.S. Pat. No. 5,081,685 discloses a license plate identification technology, wherein image intensity information is used to identify the characters on the license plate. In this technology, the characters are separated from the background on the license plate so as to obtain the outlines of the characters by a tracking process.